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This study aimed to evaluate the competitive ability of various maize, bean, and soybean cultivars when coexisting with different densities of Amaranthus hybridus, using a replacement series experiment conducted in completely randomized blocks with four replicates. The competitors included four maize cultivars, four bean cultivars, and two soybean cultivars, all tested against A. hybridus. The replacement series consisted of relative crop-to-A. hybridusratios of 100:0, 75:25, 50:50, 25:75, and 0:100%, corresponding to 20:0, 15:5, 10:10, 5:15, and 0:20 plants per pot, respectively. Competitive ability was assessed using diagrams and relative competitiveness indices. Fifty days after plant emergence, the morphophysiological characteristics of the competing species were determined. Results indicate a negative impact on all species, with both the crop plants (maize, beans, and soybeans) and A. hybridussuffering due to competition for the same environmental resources. Interspecific competition was found to be more detrimental than intraspecific competition. Maize and bean cultivars showed greater competitive ability against A. hybridus, whereas soybeans were more adversely affected by the presence of the competitor.

Ryegrass and turnip are weeds that cause high yield losses when infesting barley, thus requiring adequate management. In this context, the aim of this study was to evaluate the selectivity of different herbicide treatments and weed control in the barley crop, cultivar BRS Cauê. Two field experiments were conducted in randomized blocks, with four replications. The treatments used were: pendimethalin (800 g·ha-1), sulfentrazone + diuron (175 + 350 g·ha-1), and imazaquim (150 g·ha-1 of a. e.) applied pre-emergence; and iodosulfuron (3.5 g·ha-1), pyroxsulam (18 g·ha-1), metsulfuron-methyl (3.96 g·ha-1), 2,4-D (670 g·ha-1 of a. e.), clodinafop-propargyl (48 g·ha-1), bentazon + imazamox (600 + 28 g·ha-1), saflufenacil (49 g·ha-1), bentazon (720 g·ha-1), carfentrazone-ethyl (120 g·ha-1), and imazamox (42 g·ha-1) applied post-emergence, with two controls (one weeded and the other infested). The use of the herbicide imazaquim caused high levels of phytotoxicity in barley. Gas exchange was less responsive to herbicide applications in relation to barley phytotoxicity and productivity. Clodinafop-propargil showed the best control of ryegrass, while the herbicides iodosulfuron, pyroxsulam, metsulfurom-methyl, 2,4-D, bentazon + imazamox, saflufenacil, bentazon, carfentrazone-ethyl, and imazaquim showed high efficiency in the control of turnip species. Imazaquim caused reduction of up to 74.7% in barley grain yield. On the other hand, iodosulufuron and piroxsulam allowed the highest grain yields of the barley cultivar, BRS Cauê, by promoting partial control of ryegrass and total control of turnip species, followed by clodinafop-propargyl and metsulfuron-methyl, which controlled ryegrass and turnip, respectively, allowing an increase in yield grain in relation to the infested control. [ABSTRACT FROM AUTHOR]

The use of herbicides and weed competition can negatively affect crop yield. This study aimed to evaluate the effect of eight ALS-inhibiting herbicides and weed competition on some morphophysiological traits of oilseed rape Hyola 571 CL to determine differential herbicide sensitivity and competition with weeds. Two experiments were carried out in a greenhouse in a completely randomized block design, with four replicates. Inexperiment I, imazethapyr, imazamox, imazapic+imazethapyr, imazapic+imazapyr, pyroxsulam, and nicosulfuron decreased the photosynthetic rate of oilseed rape at first, which was later recovered. On the other hand, metsulfuron-methyl demonstrated phytotoxicity in oilseed rape and caused a marked decrease in the evaluated morphological variables. In experiment II, altered morphophysiological traits of oilseed rape were observed, with decreasing values after imazamox application and in the presence of ryegrass and/or turnip. Imazamox reduced gas exchange values after seven days, which did not affect morphological traits of oilseed rape plants after 21 days. However, the competition of oilseed rape with ryegrass+turnip caused a drastic decrease in photosynthesis rate, water use efficiency, and morphological traits. Imazethapyr, imazamox, imazapic+imazethapyr, imazapic+imazapyr, pyroxsulam, and nicosulfuron should be studied in other cultivars but showed potential to be used in weed control in oilseed rape. Competition with ryegrass and turnip was more harmful to the oilseed rape than the initial phytotoxicity caused by the herbicide imazamox.

Enlist™ technology confers resistance to 2,4-D herbicides, glyphosate, and ammonium glufosinate for soybeans. However, the application of herbicides to plants can generate stress, even in resistant crops. Thus, here we evaluated whether the application of herbicides in transgenic soybean farms, resistant to these herbicides, adversely affects the activity of antioxidant enzymes and porphobilinogen formation by delta-aminolevulinate dehydratase (ALA-D) activity. At seven days after herbicide application, the aerial part of the plants was collected and used to determine the activity of antioxidant enzymes as catalase, ascorbate peroxidase, and guaiacol peroxidase, such as lipid peroxidation levels and the activity of the ALA-D enzyme. At seven days after herbicide application, the aerial part of plants was collect and used to determine the activity of antioxidant enzymes, such as catalase, ascorbate peroxidase and guaiacol peroxidase, as well as the levels of lipid peroxidation and the activity of the ALA-D enzyme. The activity of important antioxidant enzymes involved in the scavenging of reactive oxygen species (ROS) was increased in the soybean cultivar with the Enlist™ technology, while no severe damage to lipids was detected. However, the activity of ALA-D was inhibited, which could potentially impair the formation of porphobilinogen and decrease photosynthetic efficiency. Thus, these results indicate that herbicides can affect the activity of ROS-scavenging enzymes even in transgenic, herbicide-resistant plants. [ABSTRACT FROM AUTHOR]

The study of weed interference periods and the economic threshold level (ETL) of weeds on crops allows the adoption of management methods and the rationalized use of herbicides. The objective of this study was to determine the periods of interference and to test mathematical models to determine the economic threshold level of ryegrass in the wheat crop. Two experiments were carried out in a randomized block design with four replications. The first experiment was conducted in the 2014/2015 agricultural season. The periods of interference and control of ryegrass were studied in wheat. The periods of interference and/or control were: 0, 10, 20, 30, 40, 50 and 120 days after emergence (DAE). The second experiment was conducted in the 2016/2017 agricultural season. The ETLs were studied, being the treatments composed of wheat cultivars and 12 populations of ryegrass, in competition with the respective cultivars. The results allowed concluding that the management methods of weed ryegrass must be adopted in the period between 11 and 21 days after crop emergence, which is described as a critical period of control of this weed. The wheat grain yield loss competing with ryegrass reached 59% when grown with ryegrass. For ETL, the linear regression model of the rectangular hyperbola adequately estimates grain yield losses in the presence of ryegrass. The cultivar presenting the lowest values of ETL, that is, less capacity to live with the weed, was TBIO Alvorada. The other cultivars presented similar ETL values. [ABSTRACT FROM AUTHOR]

AbstractThis study aims to evaluate the production of compounds (fungal extract) fromTrichoderma koningiopsis with herbicidal activity, as well as to analyze the effects of its application and acute toxicity using the microcrustaceanDaphnia magna. Plackett & Burman Experimental Design (PB) was selected, followed by a triplicate fermentation with the best conditions after a Central Composite Rotatable Design (DCCR 23). The dependent variables (responses) evaluated were the enzymatic activities of amylases, cellulases, lipases and peroxidases, and the fungal biomass produced was also quantified. A statistical analysis was performed on the variables to verify their significance and evaluate the validity of the proposed model. Two different fungal extracts were used for evaluation of acute toxicity, and were also applied in theEuphorbia heterophylla plant to verify the effects of phytotoxicity. Thus, the results obtained for the acute toxicity tests were EC50-48hof 58,637.99 mg/L and 13,583.17 mg/L for the first and second extract, respectively. The first one showed yellowing of the leaves of the plant. The results showed that the produced compounds are promising alternatives for reducing the use of chemical herbicides, since the microorganism showed potential for the biological control of weeds.

Copyright of Bragantia is the property of Instituto Agronomico de Campinas and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Bragantia is the property of Instituto Agronomico de Campinas and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)